A standard sandwich plate such as described in U.S. Pat. No. 3,903,663 (Bainter et al) and U.S. Pat. No. 4,555,134 (Gruna), German utility models 86 24 313, 91 05 019, or 93,19 082 or German patent documents 763,356 (Wagenseil), 3,116,938 (Lukoschek et al), 3,546,0950 (Vogt et al), 3,927,538 (Spormann), and 4,107,285 (Schmidt) has a pair of relatively hard outer skins bonded to a somewhat softer core body. The outer skins can be a hard dense synthetic resin or metal while the core can be an open- or closed-cell foam resin or a honeycomb. The plate must have a certain physical strength and must also damp sound. For the latter purpose it is standard to provide a sound-absorbing layer between one or both of the skins and the core, to provide a sound-absorbing filler between rib of the plate, or to mount the inner skin so as to minimize transmission of vibration to it from the core.
When such a plate is used in the construction of light vehicles where it must carry a load it is standard to use several of them. This is the case in, for example, magnetic-drive or cooled/refrigerated systems.
Normally the thin skins carry the longitudinally effective loads, that is loads parallel to the surfaces of the plate. The core maintains the spacing between the skins, prevents the skins from bulging, and shear in the core is effective to carry transverse loads.
In order to reduce sound transmission through such a sandwich plate it is standard to use additional sound-absorbing layers which add considerably to the construction cost of the plate. In order to suppress low-frequency sounds it is necessary to limit the transmission of vibration longitudinally in the plate. Double-wall sandwich plates transmit sound well because the skins are solidly connected to the core in the transverse direction. The connection is the result of the module of elasticity of the core and the stiffness of the air cushion captured between the skins.